Surf's Up - Indoor Wave Engineering

Allison and Vince get the lowdown on indoor surfing from the engineers at American Wave Machine. They explain the standing wave phenomenon that results from a hydraulic jump and show how designers manipulate bottom contours to give an endless ride.

American Wave Machines, a California based company has developed an innovative technology called SurfStream to provide surfers with an incredible indoor ride. Inspiration for this technology came from the idea of surfing upstream on a river and the concept of an endless ride using a standing wave.

A hydraulic jump is a phenomenon in hydraulics which naturally occurs in open channel water flow. When a fast moving flow releases into an area of lower velocity flow, it slows down very quickly and results in an increase in height, thus the kinetic energy of the flow is converted to potential energy. For this phenomenon to occur there must be a critical initial fluid speed. If the speed is not met, no jump will exist. An example of an everyday hydraulic jump is the stationary circular wave which forms around a stream of water as it flows out of a tap and contact the surface of the sink.

There are number of manifestations of hydraulic jumps. The one created by American Wave Machines is called a stationary hydraulic jump. SurfStream, engineered by American Wave Machines involves the use of a stationary submerged object which directs the moving flow upwards. The shape of the object is altered to create different types of flow. The stationary hydraulic jump is commonly generated on rivers and on engineered features like outfalls of dams and irrigation systems.

The SurfStream discharges a steady flow of water over a smooth bump referred to as a foil into into one end of the pool using a series of pumps. The stream comes into contact with a spoiler or a submerged object which the water must flow over. When enough water is discharged, the pool fills up and the hydraulic jump is established.

WhatÆs also fascinating about this technology is that the standing wave can be adjusted to different shapes, including left and right barrelling waves, stable beginner waves, and natural standing waves which are deeper and more challenging. This is accomplished by changing parameters such as incoming flow rate, the incoming channel width, and the position of the spoilers under the water. For example, if you want to change a barrelling wave from right to left, a mirror image of an angled spoiler replaces the original. The angled barrier allows the water to be pushed sideways, as well as forwards, creating a wave in which the water is pushed to one side in a curl, much like a wave found naturally in the ocean.

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